fix: maven compiler

pom.xml

@@ -20,6 +20,8 @@
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
         <spring-boot.version>2.3.4.RELEASE</spring-boot.version>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
     </properties>
 
     <dependencies>